Investigation of Groundwater Potential Using Electromagnetic Method at a Basement Complex Area of University of Abuja, Gwagwalada

Abstract

The Very Low Frequency Electromagnetic Method (VLF-EM) was used in view of detecting fractured or weathered zones within the University of Abuja Staff Quarters, Gwagwalada, Federal Capital Territory. The VLF -EM data measured along seventeen profiles of 400m at inter profile distance of 25m and interstation separation of 10m were done using the Scintrex ENVI Instrument. The VLF-EM survey revealed features significant to groundwater potential as conductive zones in the Fraser Filter maps and current density pseudosections. Three distinct zones were delineated based on the current density distribution. The fresh basement terrain corresponds to the highly resistive zone with current density value less than -20. The intermediate zone has current density value range of -20 to 25 typical of rocks and soil component which are slightly resistive to slightly conductive and corresponds to the partially saturated units. The third zone is highly conductive with current density value greater than 30 which includes the saturated weathered or fractured basement, fault zones, clay units and saturated sandy units within the study area. The north eastern, north western (profiles 1-8) and some parts of the southern region (profiles 16 and 17) of the study area show higher conductive zones than the central parts of the study area. This survey has helped in detecting sites that are suitable for groundwater exploration by identifying water bearing fractures and weathered zones in the study area. The areas with high conductivity response are areas with conductive overburden material such as clayey soil, saturated soil, water filled fractures and faults or weathered zone within the basement.